Papers belonging to Karunakaran Kandasamy, 50, who was arrested last week, offer law enforcement officers a rare opportunity to investigate who in America has donated money to the Tamil Tigers terrorist group.

Mr. Kandasamy, an American citizen, is being charged with running a front organization in Queens that prosecutors say was actually the main branch of the Tamil Tigers in America. Since last August, prosecutors have had in their possession Mr. Kandasamy’s “financial spreadsheets” detailing who gave money, and in what amounts, to the Tamil Tigers, according to the federal complaint filed last week in U.S. District Court in Brooklyn. In all, federal agents carted away “dozens of boxes” of records, propaganda, and computers last year during a search of the offices of the group, the World Tamil Coordinating Committee.

Experts have long said Tamil supporters living in America were funding the terrorist organization. Not until now have federal prosecutors brought charges alleging that to be the case. The federal government classified the Tamil Tigers as a terrorist organization in 1999.

The documents offer prosecutors the possibility of pursuing criminal charges against more than a dozen supporters of the organization across the country who are alleged to have donated money in amounts of up to $1 million, prosecutors say. Prosecutors have not yet signaled in court whether they intend to do so, and a spokesman for the U.S. attorney in Brooklyn, who brought the charges, declined to discuss the case.

The documents also present a glimpse of the relative ease with which the organization was able to raise funds.

Top donors were invited to travel to Sri Lanka, prosecutors say, to meet with the head of the Tamil Tigers, Velupillai Prabhakaran, who occupies a cultish status within the organization. In notes, which prosecutors say Mr. Kandasamy sent to Tamil Tiger officials overseas, the defendant urges that at least six donors from America get to meet with Mr. Prabhakaran, who is referred to as “the National Leader” in the letters.

The names of the individuals are redacted in the court filing. While states of residency are not provided, the court document does say that one list shows “monthly donations from numerous Tamil supporters in the tri-state area.”

The Tamil Tigers, a separatist group that controls part of northern and eastern Sri Lanka, regularly conducts suicide bombings and attempts political assassinations. A ceasefire between the organization and the government of Sri Lanka gave way in 2005 to fresh rounds of attacks.

Mr. Kandasamy is being held without bail. His attorney, Charles Hochbaum, declined to comment on the case.

The investigation that yielded Mr. Kandasamy began in 1999. It started yielding arrests last year, when 13 men, including three Americans, were charged by federal prosecutors in Brooklyn with a wide-ranging scheme to bribe State Department officials and purchase missiles in this country to shoot down military jets belonging to the Sri Lankan government.